Gang-tuned multicavity microwave tube

ABSTRACT

A continuously tunable multicavity klystron and gang tuning apparatus therefor includes a separate tuning element in association with each klystron cavity resonator for setting the respective cavity resonant frequencies. A carriage which is translated in a generally straight line path in response to the rotation of a single tuning shaft carries a plurality of elongated deformable metal bands. These bands are variable pitch cams that are followed by cam followers coupled to the tuning elements for each of cavity resonators. Each deformable band is supported on the carriage at several discrete points along the band length, and adjustment screws are provided for setting the band height and consequent tuning element contour. Such adjustment compensates for the nonlinear tuning characteristic of the cavity resonators in order to thereby obtain a resultant substantially linear cavity resonant frequency versus tuning shaft rotation characteristic. Because of the deformable nature of the bands, a smooth and continuous cam surface is formed between these discrete points.

United States Patent Merdinian et al.

[ Sept. 24, 1974 Primary Examiner-James W. Lawrence AssistantExaminerSaxfield Chatmon, Jr. Attorney, Agent, or FirmJ. D. Slobod; D.R. Pressman; S. Z. Cole [57] ABSTRACT A continuously tunable multicavityklystron and gang tuning apparatus therefor includes a separate tuningelement in association with each klystron cavity resonator for settingthe respective cavity resonant frequencies, A carriage which istranslated in a generally straight line path in response to the rotationof a single tuning shaft carries a plurality of elongated deformablemetal bands. These bands are variable pitch cams that are followed bycam followers coupled to the tuning elements for each of cavityresonators. Each deformable band is supported on the carriage at severaldiscrete points along the band length, and adjustment screws areprovided for setting the band height and consequent tuning elementcontour. Such adjustment compensates for the nonlinear tuningcharacteristic of the cavity resonators in order to thereby obtain aresultant substantially linear cavity resonant frequency versus tuningshaft rotation characteristic. Because of the deformable nature of thebands, a smooth and continuous cam surface is formed between thesediscrete points.

7 Claims, 5 Drawing Figures PATENIED SEP241974 3.838.308- SHEEI 2 OF 3GANG-TUNED MULTICAVITY MICROWAVE TUBE FIELD OF THE INVENTION Theinvention relates generally to electron beam tubes of the type whichemploy a plurality of microwave cavity resonators to interact with theelectron beam. In its particular aspects the invention relates to amicrowave tube having a plurality of cavity resonators which aregang-tuned.

BACKGROUND OF THE INVENTION In a multicavity electron beam tube such asa multicavity kylstron amplifier, typically an input microwave signal iscoupled to an input resonant cavity to velocity modulate an electronbeam. The velocity modulated beam becomes bunched as the velocitymodulation causes current density modulation in the beam. The bunchedelectron beam excites an output resonant cavity to supply an amplifiedmicrowave signal. Generally, a plurality of intermediate buncher cavityresonators are interposed between the input and output cavities forsequential interaction with the electron beam wherein each bunchercavity increases the amplitude of electron beam modulation, therebyincreasing the gain of the klystron. In such a multicavity arrangement,the input and output cavities are usually tuned to the center of adesired amplifier band, and the intermediate cavities are tuned tosomewhat different frequencies about the center frequency to shape theklystron amplifier bandwidth characteristic and consequent amplifieroutput power by stagger tuning techniques. The input and output cavitiesand the intermediate cavities thus have a pattern of resonantfrequencies in relation to the center frequency.

It is well known that the tuning of the resonant frequency of a cavityresonator may be effected by the provision of a movable tuning elementin the cavity. The tuning element may variably influence the capacitanceor inductance of the cavity or effectively vary the cavity size orshape.

One prerequisite to tuning a klystron with a structure as desired, is toprovide a means to change the resonant frequencies of the cavities bysubstantially the same amount. This is necessary since it is required tosimultaneously adjust the cavity resonant frequencies so that thespacing of each frequency about the new center frequency issubstantially preserved.

The concept of providing gang tuners" to perform this function of movingthe tuning elements for various cavities in unison in response to themovement of a single tuning shaft is well known. However, since thecavity resonant frequency is typically a non-linear function to tuningelement displacement, it has been difficult to provide a mechanicalmechanism that will faithfully provide the required linear resonantfrequency versus the tuning shaft movement. Moreover, because of thedesired pattern of cavity resonant frequencies and the normal non-linearrelationship, each cavity instantaneously tunes at a different rate.Consequently, in the prior art it has been difficult to gang tuneresonant cavities, while at the same time preserving the shape of theamplifier bandwidth characteristics.

One prior art gang-tuned multicavity microwave tube is disclosed andclaimed in U.S. Pat. No. 3,132,280, issued May 5, 1964, and assigned tothe same assignee as the present invention. This prior art deviceutilizes a plurality of flexible strands on windless drum elementscarried on a single shaft. Each of the strands is coupled to the cavitytuning elements, and upon turning the shaft, gang tune the microwavetube. This structure has given acceptable performance in previous tubes,although it has been found that for fine tuning of each element toexactly the right location over the full bandwidth, the mechanism hasleft something to be desired. Basically, the single adjustment on thedrum elements does not provide for the known variations over the rangeof frequencies that are now known to exist. Also, the structure of thelong strands does not lend itself well to a compact arrangement, thusmaking the tube assembly relatively bulky. The need for a more accurate,continuously adjustable mechanism, and one that is more compact formodern day, space limited application, has thus been identified.

Another prior art mechanism for performing the gang-tuning function isdisclosed in U.S. Pat. No. 3,617,799, issued Nov. 2, 1971, and alsoassigned to the same assignee as the present invention. This patentshows a later attempt to solve the problem of nonlinear tuning functionsof the resonant cavities and the need for simultaneously tuning thecavities in a gang by equal amounts about a central frequency. Thisprior structure, however, falls short of the present needs in thisfield, since the tuning of the various cavities cannot be continuousover a range due to the interruptions between the screw cam elements,and the range of adjustment is sorely restricted by virtue of thecircumference of the tuning wheels.

OBJECTS OF THE INVENTION It is an object of the present invention toprovide a new and improved gang tuned multicavity microwave tubeovercoming the prior art shortcoming.

It is a further object of the present invention to provide a gang tunedmulticavity microwave tube which substantially preserves a desiredpattern of cavity resonant frequencies over a relatively wide range'oftube center frequencies.

It is yet another object of the present invention to provide a tuningmechanism particularly adapted for a gang-tuned microwave tube providingcontinuous, accurate tuning.

It is another object of the present invention to provide a gang-tunedmulticavity microwave tube exhibiting a substantially linear tuningcharacteristic in response to the movement of a single tuning shaft.

It is still another object of the present invention to provide agang-tuning mechanism for multicavity microwave tubes which is compactlyintegrated with such tubes.

SUMMARY OF THE INVENTION riage has a plurality of elongated cams mountedthereon and engages a threaded portion of a rotatable tuning shaft. Eachcam, in one to one correspondence with each of the cavities. is disposedto be followed by a cam follower extension of each tuning element toeffect continuous linear tuning over the entire frequency range of thetube in response to tuning shaft rotation and consequent carriagetranslation.

Another feature of the present invention is that the cams are deformablebands which are supported by the carriage at a plurality of discretepoints along the length of eaeh band. The deformability of the bandsenables setting the cam contour to obtain a linear tuning frequencyversus tuning shaft rotation characteristic.

Still another feature of the present invention is the provision ofadjustment screws for deforming the bands at each discrete point therebyindependently setting the desired cam follower displacements. Theadjustment screws also provide means for obtaining various gainbandwidthcharacteristics from one basic tube structure.

Other objects, features, and advantages of the present invention willbecome apparent upon a perusal of the following detailed description oftwo specific embodiments thereof taken in conjunction with the appendeddrawing wherein:

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic line drawing ofthe side view of a gang-tuned multicavity klystron in accordance withthe present invention illustrating the microwave tube parts inconjunction with the tuning mechanism;

FIG. 2 is a partial cross-sectional view along the lines 22 of FIG. 1showing the gang-tuning mechanism including a cam and cam follower;

FIG. 3 is a stepped cross-sectional view along the lines 33 of FIG. 2showing the transverse section of the carriage and cams and camfollowers;

FIG. 4 is a broken cross-sectional partial view in the same direction asFIG. 2 showing an alternate cam follower embodiment; and

FIG. 5 is a view in cross section along the lines 5-5 of FIG. 4.

DETAILED DESCRIPTION OF THE DRAWING Referring to FIG. 1, the multicavitymicrowave tube of the invention is seen to comprise a klystron portionin association with a gang-tuning mechanism 11 which includes a carriage12 (see also FIG. 2). The carriage 12 is translated horizontally (intoor out of the page viewing FIG. 1) on wheels 14 to effect, by meanswhich will be fully understood as the discussion proceeds, simultaneousvertical motion of the tuning elements 17 for the various klystronre-entrant cavity resonators 16.

The multicavity klystron portion 10 is of the same general configurationas disclosed in previously cited U.S. Pat. No. 3,617,799 and includes anelectron gun portion 18 for forming and projecting a beam of elec trons20 over an elongated horizontal path to a collector electrode 22.Electron gun 18 includes a thermionic cathode 24 from which electronsare emitted. To fully accelerate the electrons in a relatively shortspace. the tube is provided with a centrally apertured anode electrode21 downstream from the cathode 24. The beam 20 passes through the anodeaperture and thereafter passes sequentially through apertures in each ofthe cavity resonators 16 prior to the beam impinging upon the collector22. Anode 21 and collector 22 are at ground potential while cathode 24is maintained at negative potential with respect to ground by dc. powersupply 23. As is usual. a magnetic focusing structure (not shown)coaxial with the electron beam 20, provides an axial magnetic fieldalong the beam 20 to confine the cross section of beam 20 during itspassage through the region including all of the cavity resonators 16.

The first cavity resonator encountered by electron beam 20 is the inputcavity 26 to which an input microwave signal is coupled via input line28 to velocity modulate electron beam 20. A plurality of buncherresonant cavities 30 are sequentially encountered by electron beam 20which thereafter encounters output cavity resonator 32. Each bunchercavity increases the microwave modulation of the electron beam toincrease the gain of the klystron l0 and consequentlythe amplitude ofthe output microwave signal which is extracted from the output cavityresonator 32 via coupling 34.

The various cavity resonators 16 are not generally tuned to exactly thesame microwave resonant frequency, but rather are tuned to slightlydifferent frequencies about a microwave center frequency to shape thegain-bandwidth characteristic of the amplifier by stagger tuningtechniques. Typically, the input and output cavity resonators 26 and 32,respectively, are tuned to the microwave center frequency and thebuncher cavity resonators 30 are tuned to various microwave frequenciesabout the center frequency to generate the intended passband of klystronamplifier l0.

Tuning elements 17 for changing the cavity resonant frequencies arepreferably plungers which project into the cavity resonators l6 andwhich are mounted for vertical movement. In particular, the tuningelements 17 are preferably sliding shorts for changing the electricallength of the cavity resonators 16. A suitable sliding short-type tuningplunger is disclosed and claimed in U.S. Pat. No. 3,618,518, issued Oct.19, 197], and assigned to the same assignee as the present invention.Other tuning elements which are essentially probes for influencing thecavity resonator inductance or capacitance are suitable or the purposesof the invention. In addition, tuning elements of the type which bearupon and deform a wall of the cavity resonators may be used. Whatevertuning element type is used, an actuating rod portion or equivalent 36is fixedly attached to the tuning element for moving the elementvertically in the orientation of the figures and perpendicularly to thebeam 20. The rods 36 protrude vertically through an aperture 37 in thecavity resonators 16. Each actuating rod 36 also passes through a vacuumsealing bellows 38.

At the bottom ends of the actuating rods 36 are carried cam followingrollers 40. Each roller 40 rides upon an associated inclined cam 42carried by the carriage 12. As the carriage is translated horizontallyand perpendicularly to the beam 20, the cam following rollers 40 foreach actuating rod are driven in unison, but by different amounts asadjusted. Responsively, the plungers 17 are moved in a manner to changethe center frequency of the tube while substantially preserving theintended frequency spacing between the various cavity resonantfrequencies, thereby substantially preserving the intendedgain-bandwidth characteristics of the klystron 10.

Referring next to FIGS. 2 and 3, the mechanical parts of the gang tuningmechanism will be better understood. The mechanical parts of thegang-tuned klystron are enclosed in a housing 44 of a non-magneticmaterial, so as not to influence the electron beam direction. Similarly,all mechanical parts are preferably nonmagnetic.

The carriage 12 comprises an elongated plate 46 which carries theplurality of spaced apart elongated inclined cams 42, with each cam 42disposed below one of the cam following rollers 40. A threaded block 48is fixedly attached to the bottom of plate 46 by screws 50. A rotatabletuning shaft 52 passing through the block 48 is journalled at oppositesides of the housing and is driven by a crank type tuning knob 54external of the housing to effect translation of the carriage 12. Themajority of the shaft 52 is externally threaded for translating theblock 48 and consequently the carriage 12 parallel to the tuning shaft52. At the point where the tuning shaft 52 exits the housing 44, thetuning shaft passes through a collet member 56 retained by the housing.The member 56 may be tightened upon the tuning shaft by a coaxiallysurrounding conically apertured locking knob 58. This combination locksthe angular position of the tuning shaft, and consequently the positionof the carriage 12 along its horizontal path of movement. The cams 42are inclined (see FIG. 2) in the direction of carriage movement forvertically moving the actuating rods 36 as the carriage is translated.

Any tendency for horizontal movement, such as the downward pushing forceof the rollers 40 on the in clined bands, is prevented by the lockingknob 58 when activated.

Below the plate is fixedly attached the shafts 60 for the four wheels14. The wheels 14 ride upon atop horizontal surface 62 provided by twolaterally spaced apart blocks 63. Blocks 63 are supported by the base ofthe housing 44 and one of the blocks 63 is provided with an elongatedslot 64 in the surface 62 running the length of intended carriagetranslation. The two wheels on the side of'the carriage above the oneblock are pro vided with a radial flange 66 which projects into the slot64 to provide a track for laterally guiding the carriage 14.

Above the carriage plate 12 are a plurality of spaced apart cam carryingblocks 68. The cam carrying blocks 68 are each supported at oppositeends on the tops of screws 70, which are threaded vertically upward intothe plate 46. Screws 71, threaded into block 68 from the underside ofplate 46, draw the blocks 68 downward against the screws 70. The screws70 permit the independent adjustment of the general or concerted inclineof each of the blocks 68, and consequently the gang adjustment of thecams 42 carried by the blocks.

The earns 42 are pinned to the block at opposite ends 73 with pins 72and springs 76 are stretched between the pins 72 and corresponding pins74 fixedly carried by the plate 46. This arrangement forces the block 68against the inclined setting screws 70 during the time when screws 71are loosened to permit adjustment. Consequently, the cam followerdisplacement at the two end points of the cam may be independently setby simply adjusting the screws 70.

The elongated earns 42 are each relatively thin deformable metal bands.At a plurality of intermediate points 77 along the cams 42, projectionsare provided on the underneath side, and threaded support rods 78 arepinned to the cam. This structure provides a means for deforming theshape of the cams to the nonlinear but smooth contour required tocontinuously compensate for the inherent nonlinearity in eachindependent cavity tuning characteristic. This unique combination ofelements allows independent setting of the cam follower displacement atthese intermediate points, and thus the infinite range of contoursrequired.

Axially bored screws 79 are internally, as well as externally, threadedwith threads of slightly different pitches. The outer threads engagecorrespondingly threaded holes in the block 68. Each of the support rods78 is threaded by engaging the internal threads of a corresponding screw79. Rotation of the screws 79 permits a very fine vertical adjustment ofthe height of each of the points 77 with respect to the block 68.Consequently, utilizing adjustment screws and 79, the vertical height ofthe cams at a plurality of discrete points along the cam length may beadjustably set to gain the variable relationship required non-linearcompensation described above.

To explain further, it is convenient to consider the horizontal surface62 on which the wheels of the carriage ride as a reference plane. [t isclear that the various adjustment screws carried by the carriage 12provide means for independently, separately adjusting the height of thecam surface with respect to the reference plane at each of a pluralityof discrete points along the length of the cam. The deformable featureof cams 42 enables the adjustment of cam height at the interior discretepoints 77 since if the cams were not deformable, adjustment would onlybe possible at two points such as the end points 73. The continuousnature of the bands 42 allows the desirable infinite coordinatedadjustment of the elements 17 over the design range of the tube, ratherthan only spaced, incremental adjustments, as in the prior US. Pat. No.3,617,799, cited supra.

Each actuating rod 36 passes through the aperture 37 in cavity resonatorlower wall 80 (see FIG. 2), then through a first apertured plate 82below the cavity wall, and thereafter through a second apertured plate84, forming a portion of the enclosure 44. The actuating rod 36 slidesin a bushing 86 for vertical guiding action. A radially flanged cylinder88 is fixedly attached coaxially to actuating rod 36 between the firstand second plates to provide a stop against the top of the second plate84. This stop is provided to prevent any damage of the associated tuningelement when maximum lower end adjustment is reached or if the carriageparts are removed. The actuating rods 36 are pinned to a third plate 90just above the rollers 40, and independent compressed spring pairs 92act between the fixed first plate 82 and each plate 90 carried by eachof the actuating rods 36 to force each cam follower roller 40 againstthe corresponding cam 42. The springs 92 are mounted on axiallytelescoping rod and tube combinations 93a and 93b, respectively, and thesame pass through large apertures 94 in the second plate.

Reference is next made to FIGS. 4 and 5 where two views of an alternate,cam capturing cam follower 101 is shown. Therein, the end of theactuating rod 36 is fitted with ears enclosing a generally rectangulararea 102 through which the cross section of the cam 42 fits. A ballseated in an axial bore 104 in the actuating rod is forced by spring 105tightly into engagement with the cam surface, in turn lifting the bottomof the cam 42 against a bottom interior surface 106 formed by the ears100. Capture of the cams 42 in the cam follower prevents any possibilitythat the cam followers will not ride along the centers of the narrowcams 42 or drop off the cams 42 altogether.

It is clear that numerous modifications are possible within the spiritand scope of the invention, For example, the cams 42 could be carried bythe actuating rods 17 and the carriage 12 could carry the cam followers.

While there has been described and illustrated several specificembodiments of the invention, it will be clear that variations in thedetails of the embodiments specifically illustrated and described may bemade without departing from the true spirit and scope of the inventionas defined in the appended claims.

What is claimed is:

1. A continuously tunable microwave tube apparatus comprising:

a housing;

electron gun means within said housing for forming and directing a beamof electrons over an elongated path;

a plurality of cavity resonators, within the housing,

arranged along the beam path for successive electromagnetic interactionwith the beam;

a movable tuning element associated with each cavity resonator foradjustably setting the resonant frequency of each cavity;

a plurality of movable cam followers, each follower coupled to acorresponding one of the tuning elements, whereby the resonant frequencyof each cavity resonator is variable by the motion of a correspondingcam follower;

a movable tuning shaft having an operative portion within the housing;

a carriage mounted for translation along a generally straight pathdefined by an axis within said housing, said carriage having means forengaging said operative portion in a manner so that the carriage istranslated in response to movement of said tuning shaft; and

a plurality of elongated cams on the carriage, said cams being inclinedwith respect to the carriage axis, each cam being disposed to befollowed by a corresponding one of the cam followers, and means to shapesaid cams to provide a substantially linear cavity resonant frequencyversus tuning shaft characteristic.

2. The apparatus of claim 1 wherein the electron gun means forms anddirects an electron beam along a substantially straight path, saidcarriage axis being perpendicular to the beam path.

3. The apparatus of claim 2 wherein the cams are elongated, deformablebands mounted on the carriage at discrete points along the bands.

4. The apparatus of claim 3 wherein said means to shape the bandscomprises means for deforming the bands so as to adjust the position ofeach cam follower at each of the discrete points.

5. The apparatus of claim 4 wherein the tuning shaft is mounted forrotation in combination with a tuning knob external of said housingcoupled to the tuning shaft for rotating the shaft.

6. In combination with a microwave tube having a resonant cavity inenergy exchange relationship with an electron beam gun, and a movablefrequency tuning element in association with the resonant cavity, and acam follower coupled to said tuning element, the tuning mechanismcomprising:

a cam movable with respect to said cam follower along a path defining anaxis, said cam comprising an elongated deformable band upon which saidcam follower rides, said cam being continuous and inclined with respectto said axis, tuning means for translating said cam to said axis, tuningmeans for translating said cam to adjust said tuning element in saidcavity; and

means for individually adjusting the distance of the band from the axisat a plurality of spaced apart discrete points along the band length,whereby said cams may be shaped to provide a substantially linear cavityresonant frequency versus tuning means motion characteristic.

7. The tuning mechanism of claim 6 wherein said means for translatingthe cam moves along a substantially straight path.

1. A continuously tunable microwave tube apparatus comprising: ahousing; electron gun means within said housing for forming anddirecting a beam of electrons over an elongated path; a plurality ofcavity resonators, within the housing, arranged along the beam path forsuccessive electromagnetic interaction with the beam; a movable tuningelement associated with each cavity resonator for adjustably setting theresonant frequency of each cavity; a plurality of movable cam followers,each follower coupled to a corresponding one of the tuning elements,whereby the resonant frequency of each cavity resonator is variable bythe motion of a corresponding cam follower; a movable tuning shafthaving an operative portion within the housing; a carriage mounted fortranslation along a generally straight path defined by an axis withinsaid housing, said carriage having means for engaging said operativeportion in a manner so that the carriage is translated in response tomovement of said tuning shaft; and a plurality of elongated cams on thecarriage, said cams being inclined with respect to the carriage axis,each cam being disposed to be followed by a corresponding one of the camfollowers, and means to shape sAid cams to provide a substantiallylinear cavity resonant frequency versus tuning shaft characteristic. 2.The apparatus of claim 1 wherein the electron gun means forms anddirects an electron beam along a substantially straight path, saidcarriage axis being perpendicular to the beam path.
 3. The apparatus ofclaim 2 wherein the cams are elongated, deformable bands mounted on thecarriage at discrete points along the bands.
 4. The apparatus of claim 3wherein said means to shape the bands comprises means for deforming thebands so as to adjust the position of each cam follower at each of thediscrete points.
 5. The apparatus of claim 4 wherein the tuning shaft ismounted for rotation in combination with a tuning knob external of saidhousing coupled to the tuning shaft for rotating the shaft.
 6. Incombination with a microwave tube having a resonant cavity in energyexchange relationship with an electron beam gun, and a movable frequencytuning element in association with the resonant cavity, and a camfollower coupled to said tuning element, the tuning mechanismcomprising: a cam movable with respect to said cam follower along a pathdefining an axis, said cam comprising an elongated deformable band uponwhich said cam follower rides, said cam being continuous and inclinedwith respect to said axis, tuning means for translating said cam to saidaxis, tuning means for translating said cam to adjust said tuningelement in said cavity; and means for individually adjusting thedistance of the band from the axis at a plurality of spaced apartdiscrete points along the band length, whereby said cams may be shapedto provide a substantially linear cavity resonant frequency versustuning means motion characteristic.
 7. The tuning mechanism of claim 6wherein said means for translating the cam moves along a substantiallystraight path.